[TowerTalk] Grounding

[jimlux]

On 9/4/19 10:35 AM, David Gilbert wrote:
> 
> The fine print on every whole house surge protector I've been able to 
> find specifically excludes lightning for coverage.  The coverage 
> specifies only power line surges.  Are you aware of one that includes 
> lightning?
> 

I think that the value of the whole house protector is in reducing the 
amplitude of spikes that are *induced* by a nearby lightning strike, as 
opposed to dealing with the *direct* effect of a strike.

For instance, lightning current flowing in your tower or ground system 
inducing a voltage in power wiring in your wall that is parallel to the 
tower, even with no physical connection.

There's a lot of ways to kill equipment with fairly small, but fast 
transients.  Tesla coils are notorious for this, since the "sparks" are 
about 5-6 feet long, discharging a 20-50 pF capacitor really fast (2 
microhenry inductance from the spark), so you get this nice high di/dt 
which induces differential voltages in the loops formed by the 3rd wire 
grounding of appliances and the like.

A lightning strike can do the same thing - the main stroke causes 
induced voltages in near by objects, which then breaks down as a 
separate discharge, with really high di/dt (higher than the lightning 
stroke itself, because the inductance in the circuit is lower than in 
the lightning stroke)



> Dave   AB7E
> 
> 
> 
> On 9/4/2019 8:44 AM, john at kk9a.com wrote:
>> GL rebuilding Keith.
>>
>> A tower lightning strike will cause an induced voltage spike in a 
>> home's electrical system, even if nothing is connected to the tower. I 
>> have had this occur while building a new tower and the control cables 
>> and coax were not yet connected or even touching the tower. Simply 
>> disconnecting the coax which many hams do is ineffective lightning 
>> protection. There is a lot of valuable protection information on this 
>> list. Assuming that you have a bunch of ground rods and a SPG, I would 
>> suggest a good whole house surge protector.
>>
>> John KK9A
> 
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